At the same time, Defence Secretary Des Browne was raising hopes of an early withdrawal of the 7,000 British troops. In a keynote speech, he will say the handover of military control in Basra next spring will be a "decisive change" in the UK involvement. Mr Browne will say that the role of troops will shift to providing back-up to the Iraqi army and police and helping to protect supply routes.

He will pledge that Iraqi forces will not be asked to take on too much too quickly but that British forces will not stay longer than necessary.

Hopes of a phased withdrawal starting next summer depend on Iraq's security forces being able to contain insurgents.

Mr Cameron and foreign spokesman William Hague were being briefed this morning by General Richard Shirreff, the British commander in the south of Iraq before meeting troops.

They were planning to hold talks with Iraqi politicians tomorrow. Mr Cameron said his first purpose was to support the troops and hear their views.

He added: "The second is to get a more direct understanding of the political situation by meeting Iraqi politicians and to look at the prospects for halting the terrible cycle of violence and for making the transition to Iraqi control over security."

Senior Tories dismissed claims that he had "snubbed" the CBI. They said the Iraq trip had been due on 8 November but was postponed by the Ministry of Defence for logistical reasons. Today was the first date both Mr Cameron and the MoD could manage. Shadow chancellor George Osborne stood in for him.

Foreign Secretary Margaret Beckett has told the Commons that Iraqi authorities will be able to take over Basra in the spring. However, a UN report has said the Iraqi death toll hit a record high last month, with more than 3,700 people killed in continuing violence.

Meanwhile, the former UN inspector who correctly said there was no evidence that Iraq had weapons of mass destruction will today criticise Tony Blair. Hans Blix will argue that the decision to replace Trident will make it harder to stop Iran from acquiring a nuclear bomb.

In a speech in London, he will claim that renewing Britain's independent deterrent will put the non-proliferation treaty under "strain" and make nonnuclear countries like Iran feel "cheated". The Cabinet last week agreed to start the process of ordering a new nuclear weapons system at a cost of £25 billion.